Pigment preparation for coloring polymers

ABSTRACT

The invention relates to a pigment preparation for coloring polymers. The inventive preparation comprises one or more pigments and a carrier. According to the invention, the carrier includes an oligomer or a combination of low-molecular-weight polymers from the group containing polymers and copolymers of ethylene-acrylic acid, ethylene-maleic anhydride or polypropylene-maleic anhydride. The carrier also includes a polymer from the group containing polymers of ethylene-ethyl acrylate, ethylene/butyl acrylate, ethylene/methacrylic acid, polypropylene with grafted methyl polymethacrylate, polypropylene with grafted polystyrene or block copolymers of styrene. For organic pigments, the preparation contains 50%-70% pigment and 50%-30% carrier. For inorganic pigments, the preparation contains 60%-90% pigment and 40%-10% carrier. The invention comprises a polyvalent pigment preparation which can be used in the production of color concentrates with specific bases and high precision.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention refers to a pigment preparation used as an intermediaryproduct for dying polymers, the advantages of which has numerousbenefits, as detailed in this report.

The invention belongs to the technical area of plastics, in particulardying polymers.

2. Brief Description of the Related Art

Colour concentrates are normally used to dye polymers, called“masterbatch” in the technique. The advantages of using colourconcentrates, with regard to other systems, such as dry dying, aredescribed below.

The process of polymer dry dying is carried out by simply physicallymixing pigments with the polymer. The pigment powder particles have astrong tendency to group together and to form strongly cohesive clumps.These are difficult to separate using a transformation process. Inconsequence it is normal that the dyed material has spots and colourstains. This process cannot be used on thin materials (film, raffia,fibre, laminate . . . ) or where how the material looks is critical.

In the case of colour concentrates, there are pigment dispersions in theform of very fine particles which are included into a plastic mediumsimilar to the resin to be dyed or a medium which is compatible to thesame. Highly uniform and high-quality dyes are obtained due to theoptimum dispersion of the pigment.

Typical colour concentrates are in the form of granules and theconventional concentration is between 5-30% for organic pigments and15-60% for inorganic pigments. Usage dosage is between 2-4% depending onthe transformation system for the resin to be dyed as well as thethickness of the final article. In general, colour concentrates are usedin processes which require a prior mixture of the material to be dyed ina spindle such as during the injection, extrusion, extrusion-blowing etcmoulding processes.

Color concentrate production can be carried out using different methods:

1—From a powder pigment: production is in two stages. During the firstphase the pigments, spreaders, lubricants, stabilisers and otheradditives are mixed with the resin, usually in turbo mixers or by usinga gravimetric analysis. During the second stage the finished product isobtained by excluding the pre-mixture using a twin spindle co-rotatingextruder.

2—Using single colour concentrates: in this case single pigment colourconcentrates are obtained using the method described in the abovesection during the first phase. The final colour concentrate is obtainedby extruding the physical mixture with the support polymer (normallyusing a single spindle extruder). The pigment concentration of thesingle colours is usually between 15-40% for organic pigments andbetween 40-70% for inorganic pigments. These single colour concentratesare compatible with a very limited family of polymers.

3—Using pigment preparations: the pigment preparations have an optimumdispersion of a pigment in an organic medium. The concentration istypically 40-50% for organic pigments and 50-80% for inorganic pigments.The drawback for single colour concentrates is that they have a limitedcompatibility. In practice, the use of pigment preparations is limitedto polyolefinic polymers, some elastomers and with restrictions inpolyamide. The final colour concentrate is usually obtained by extrudinga physical mixture of the pigment preparations and the support polymerin a co-rotating dual spindle extruder. As opposed to single colourconcentrates, pigment preparations are physically micro-granules whichare obtained from the pigments in the form of a pressed filter aqueouspaste. This paste is placed in a vacuum mixer. Small amounts of specialadditives are added to quickly remove water and moisture from thepigment particles by using the organic substrate (oils, waxes,plasticisers, polymers, etc).

If there are universal colour concentrates, which are theoreticallycompatible with all polymers, their use in practice is restricted to thetype of application.

For dying critical articles or during critical applications, the use ofspecific colour concentrates is required together with the same orchemically very similar support as the resin to be coloured.

It is necessary to find the optimum combination of spreaders,stabilisers, lubricants, etc for each support during the manufacture ofcolour concentrates with specific bases. This means that themanufacturer of colour concentrates or dying compounds (particularly fortechnical polymers) must use many formulas and manufacturing processes.

It would be much easier if there were multipurpose pigment preparationswhich could be used to manufacture colour concentrates with specific andhighly accurate bases.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention proposes multipurpose pigment preparations which, whenmixed with any polymer resin and by using an extrusion process (twinspindle co-rotating extruder), allows colour concentrates with specificbases to be obtained.

The pigment preparations in this invention are obtained using atwo-stage process: premixing and simple extrusion resulting in 3 mmgranules or preferably micro-granules with a diameter of less than 1.2mm.

More specifically, the single pigment colour concentrates in theinvention have the following chemical composition:

Organic Pigments:

-   -   50-70% pigment    -   50-30% carrier

Inorganic Pigments:

-   -   60-90% pigment    -   40-10% carrier

The carrier has a first component selected from the following group:

polymers or copolymers of ethylene acrylic acid;

polymers or copolymers of ethylene maleic anhydride;

Polypropylene maleic anhydride;

Polycaprolactone; and

mixtures or combinations thereof.

The carrier also includes preferably one or more of the followingpolymers:

Polymers of ethylene acrylic acid;

Polymers of ethylene butyl acrylate;

Polymers of ethylene methacrylic acid;

Polypropylene grafted with polymethyl methacrylate (PMMA-grafted PP);

Polypropylene with grafted polystyrene (PS-grafted PP);

Block copolymers of styrene; and

mixtures and combinations thereof.

The use of the aforementioned pigment preparations considerablysimplifies the colour concentrate production process. In order to obtainthe pigment preparations just the physical mixing of different pigmentswith the base polymer is required followed by processing in a twinspindle co-rotating extruder. The premixing process in a turbo mixer isnot required using this process and therefore the complexity of studyingand selecting from a recipe of spreaders, stabilisers, lubricants, etcfor each polymer is avoided.

By using the invention, it is also possible to simplify the colourequaling process. Premixing pigments, additives, etc is also notrequired during the production process and the development process of anew colour. In this way, the colour duplication process is simpler andquicker.

Another advantage of the invention is that the same intermediateproducts are used, due to the preparation phase in the laboratory andthe production phase in the factory. The change of scale betweenlaboratory and reduction is thereby avoided.

The high concentration of pigments in the invention allows costs to bereduced and flexibility in simplifying the production process to beincreased. Also the product in the invention is a multipurpose productmeaning that it can be used for all polymers (LDPE, LLDPE, HDPE, PP—homoand copolymer—, PVC—rigid and plasticised—, PS, ABS, ASA, SAN, CAB, PA,PC, PET, PBT, etc).

In this way, the carrier is also multipurpose and is compatible with themajority of commercial polymers with the ability to be mixed with itselfor with any other polymer in any proportion with a carrier in order toobtain a highly accurate, specific colour concentrate.

Having sufficiently described how this invention, it is easy understoodthat any modification to the detail of the mention which is judged to besuitable may be made whenever the essential features of the summarisedinvention in the following claims are not altered.

1. A pigment preparation for dyeing polymers, consisting of: at leastone pigment and a carrier, the carrier consisting of: a first componentselected from the group consisting of ethylene-acrylic acid copolymer,ethylene-maleic anhydride copolymer, and polycaprolactone polymer; and asecond component selected from the group consisting of ethylene-ethylacrylate copolymer, ethylene-butyl acrylate copolymer,ethylene-methacrylic acid copolymer, Polypropylene grafted withpolymethyl methacrylate copolymer, polypropylene with graftedpolystyrene copolymer and block copolymers of styrene; wherein thepigment preparation is a chemical composition of between 50% and 90% ofthe pigment and between 10% and 50% of the carrier.
 2. The pigmentpreparation according to claim 1, wherein the pigment is an organicpigment, and the pigment preparation is a chemical composition ofbetween 50% and 70% of the pigment and between 50% and 30% of thecarrier.
 3. The pigment preparation according to claim 1, wherein thepigment is an inorganic compound, and the pigment preparation is achemical composition of between 60% and 90% of the pigment and between40% and 10% of the carrier.
 4. The pigment preparation according toclaim 1, wherein the pigment is selected from the group consisting oforganic pigments, inorganic pigments and any combination thereof, andthe pigment preparation is a chemical composition of between 50% and 90%of the pigment and between 50% and 10% of the carrier.